Rendering unconnected edges
Cycles

I don't know of any way to render edges like this natively in cycles, however the screw modifier can add geometry to edges:



It's a bit of hack, but I don't know of any faster way to add faces to edges using modifiers (it's not actually that bad, in most other cases using the screw modifier you would probably use only edges anyway).

Blender Internal

You can render edges using a Wire material:



Opengl

Of course, the viewport can render edges, however you are pretty limited in terms of controlling the color..



This patch may help though.